Motion mechanism of X-ray film in panoramic radiography

Abstract

This invention relates to a motion mechanism for moving an X-ray film in a panoramic X-ray machine in a predetermined pattern and rate of travel relative to a source of radiation. The mechanism includes a cassette holder on which is carried a rotatable rod or roller driven by a traction wheel, a lever assembly for changing the drive angle between the traction wheel and the rod and a moving or rotatable supporting column or structure on which the motion mechanism is mounted. The panoramic X-ray machine also has a radiation source suspended from one end of the supporting structure at a position opposite the cassette holder. The object or patient to be radiographed is placed between the radiation source and the cassette holder and the supporting structure is rotated at a selected rotational speed about the object.

I claim: 
     
       1. A mechanism for moving a planar X-ray sensitive film cassette in a panoramic X-ray system having a stationary frame, a rotatable support arm supported by the stationary frame, an X-ray source attached to one end of the rotatable support arm, and a film cassette holder attached to the opposite end of the rotatable support arm, the film cassette holder adapted to receive the planar film cassette for linear movement relative to the rotatable support arm; said mechanism comprising:   (a) a rotatable rod supported by the film cassette holder with the longitudinal axis thereof parallel to the plane of the film cassette;   (b) a traction wheel in frictional driving engagement with said rotatable rod, said traction wheel having a rotational axis;   (c) means for rotating said traction wheel; and   (d) means for varying in a predetermined manner the angle between the rotational axis of said traction wheel and the longitudinal axis of said rotatable rod; whereby the linear speed of the film cassette relative to the rotatable support arm during radiographic exposure is varied in a predetermined manner which is dependent upon the angle between the longitudinal axis of said rotatable rod and the rotational axis of said traction wheel.     
     
     
       2. The mechanism of claim 1 wherein said varying means comprises: (a) cam means secured to the stationary frame,   (b) cam follower means in coacting contact engagement with said cam means, and   (c) linkage means mounted on said rotatable support arm interconnecting said cam follower means and said traction wheel for varying the angle between the rotational axis of said traction wheel and the longitudinal axis of said rotatable rod as said cam follower means moves in contact with said cam means.   
     
     
       3. The mechanism of claim 2 wherein: (a) the axis of said cam means is coincident with the rotational axis of the rotatable support arm.   
     
     
       4. The mechanism of claim 2 wherein said linkage means comprises: (a) a first lever slidably mounted on the rotatable support arm, said first lever having a first end and a second end, said cam follower means being mounted on said first end, and   (b) a second lever havinga first end pivotally connected to the second end of said first lever, and a second end connected to said traction wheel.   
     
     
       5. The mechanism of claim 4, including: (a) lost motion means intermediate the first and second ends of said first lever.   
     
     
       6. The mechanism of claim 1 wherein: (a) said traction wheel is rotated at a speed in a predetermined synchronous relation with the rotational movement of the X-ray source attached to the rotatable support arm.   
     
     
       7. The mechanism of claim 1 wherein: (a) the angle between the longitudinal axis of said rotatable rod and the rotational axis of said traction wheel is varied in a manner which is dependent upon the angular position of the X-ray source relative to the axis of rotation of the rotatable support arm.